Bug sex: the top five most bizarre invertebrate sexual practices

Many species of spider are cannibalistic -- namely, the female
eats any suitor who tries to impregnate her. As such, the male of
the species appears to have accepted its fate: instead of battling
the inevitable, he has come up with novel methods of ensuring as
much sperm gets in the female as possible. Enter the fascinating
world of spider self-castration. All male spiders, including white
widows, are equipped with pedipalps -- penis-like appendages that
are used to penetrate the female and get the goods to the sperm
storage organs.

"Here, it's all part of the same desire of a male wanting to
keep his sperm in there and keep other male's out," says Bondar.
"With the isopods it was guarding, and for the white widow it's a
type of mate-plugging."

"Once he's transferred the sperm into the female's reproductive
opening with his pedipalp, he will break it off." Gulp. "So now
he's without a pedipalp and it's stuck in the female's opening.
It's the equivalent of a man breaking off his penis in the vagina
and hoping this will be an effective barrier to any other future
sperm deposits. And in the white widow it actually is. It's an
effective way for him to exclude other males from making deposits
into her."

According to a 2012 study, the method actually enables the male to get
more sperm into the female. A team of evolutionary biologists
monitored wild virgin female spiders and dissected them
post-copulation to discover that the breaking of the pedipalp
ensured continual sperm transfer -- even post-detachment. The biologists asserted it was an evolutionary tactic developed to
counter the female's murderous tendencies and typically brief
duration of copulation.

"In spiders you'll see a trend of a very, very large female and
a tiny male," says Bondar. "Again, as is the case with many
cannibalistic species, the male has to sneak in there and be so
careful."

"In another species the male actually cinches his waist up and
has the effect of displacing the vital organs to the outer
periphery so when he rolls in there and tries to impregnate the
female, she'll bite him, but because a lot of the organs have been
displaced he lives through the first reproductive bout and can come
back for a second."

In the case of the white widow, the male actually has a spare
pedipalp, however he rarely gets the chance to use it.

"The unfortunate reality for many white widow males is that he
has a good chance of getting eaten right then and there," says
Bondar. "Chances are it's the end of the road for them; she eats
them."

Mate plugging does in fact even occur in some primates. In the
Madagascan
mouse lemurs, males use a sticky substance to cover the
female's vagina post-copulation. It hardens and acts as a barrier,
preventing other males in the group from having a go.

"Invertebrates take it to the max though," says Bondar.
"Actually breaking off your reproductive appendage is pretty darn
extreme. They're in it for the win."